1. The first thing you can do is to check the dial tone. If you do not hear any dial tone, the problem is with your computer.
2. Try unplugging all phone devices and connect just the modem and try to go online.
3. Try restarting your computer and modem after unplugging the cords and leaving it still for some minutes.

If you still see problems, you can contact AOL tech support to acquire the help of expert technicians to solve the problem for you remotely.